This invention relates to a high pressure sensor for an automotive system, and more particularly to a low cost three-piece sensor assembly having a stainless steel pressure sensor element.
Motor vehicle controls frequently require measurement of certain pressure parameters such as engine oil pressure, fuel pressure, transmission fluid pressure or brake pressure. For this reason, it is customary to attach high pressure sensors to various pressure vessels in the vehicle. High pressure applications generally utilize a stainless steel pressure sensor element welded to a pressure port that is attached to the pressure vessel by a threaded fitting, for example. To enable reliable welding of the sensor element to the pressure port, the pressure port must also be formed of stainless steel material.
Due to the high cost of stainless steel relative to other materials, and the difficulty of machining stainless steel, various pressure port configurations have been developed for minimizing the required amount of stainless steel. For example, the U.S. Pat. No. 5,939,637 to Pitzer et al., issued on Aug. 17, 1999 and assigned to the assignee of the present invention, discloses a three-piece pressure port comprising a casing formed of cold-rolled steel, a small stainless steel insert staked into a recess on one end of the casing, and an O-ring sandwiched between the casing and the insert to form a seal. In another configuration disclosed in the U.S. Pat. No. 6,050,147 to Viduya et al., issued on Apr. 18, 2000 and assigned to the assignee of the present invention, the casing is formed of stainless steel, and a hexagonal ring formed of cold-rolled steel is coupled to the outer periphery of the casing to enable installation and removal of the sensor assembly. In each case, the sensor element is welded to the stainless steel component of the pressure port, and an axial bore places the sensor element in communication with the interior of the pressure vessel to which the casing is attached.
While the above-mentioned configurations reduce the cost of the pressure port by minimizing the usage of stainless steel, a significant portion of the overall sensor cost is attributable to the welding of the sensor element to the pressure port. Accordingly, the cost of the sensor could be reduced even further if the welding operation could be eliminated.
The present invention provides an improved three-piece pressure sensor assembly including a one-piece pressure port formed of cold rolled steel, a stainless steel sensor element having an elongated annular side-wall, and an O-ring. The pressure port has a threaded slug at one end for attaching the sensor assembly to the wall of a pressure vessel and an annular cup at the other end. The annular cup has side-walls defining a cavity, and an annular axial recess formed in the center of the cavity receives the O-ring and a lower portion of the sensor element side-wall. A central post of the pressure port supports the inner periphery of the sensor element side-wall, and a portion of the pressure port material surrounding the recess is displaced radially inward against the sensor element side-wall, staking the sensor element in the cavity and compressing the O-ring between the sensor element and the bottom of the axial recess. An axial opening through the central post of the pressure port places the sensor element in communication with the interior of a pressure vessel to which the assembly is attached.